In an amplifier for producing short-pulse CO2 laser light having a pulse width of 100 ns or less, a CO2 laser gas which is excited by continuous-wave (CW) discharge is cooled by means of forced convection, and the direction of the gas flow caused by the forced convection is substantially the same as that of the optical axis of the laser light to be amplified (See, e.g., Patent Document 1). In other words, a high-speed axial flow type of carbon dioxide gas laser has been conventionally used (See, e.g., Non-patent Document 1).
In the high-speed axial flow type of CO2 gas laser, a laser gas is excited inside a cylindrical discharge tube. The laser gas is flown from one end to the other end of the cylindrical tube. The optical axis of the laser light is also set in parallel with the central axis of the cylindrical tube. In other words, the direction of the laser gas flow is arranged in parallel with the optical axis. The direction of the laser gas flow refers to a direction in which most of the laser gas flows among the laser gas present in a discharge region defined by the shape of discharge electrodes. Henceforth, unless otherwise stated, the direction of the gas flow will refer to the above-described meaning.
In case of using the CO2 gas laser as an amplifier, it only needs to replace the resonator mirrors with windows. In other words, laser light generated from an oscillator is amplified by the laser gas excited in the amplifier. The laser gas cools the CO2 laser gas by forced convection and the direction of the gas flow caused by the forced convection is substantially the same as that of the optical axis of the laser light to be amplified.
In Patent Document 1, a pulse CO2 laser with an output power of 10 W is arranged at an oscillation stage and two continuous wave (CW) CO2 lasers are arranged at an amplification stage. The pulse CO2 laser at the oscillation stage can generate pulsed light at a high repetition frequency (for example, 100 kHz). In this example, the pulse CO2 laser at the oscillation stage operates in a single-transverse mode to generate a laser beam having a wavelength around 10 μm. The pulsed light having a lower power generated from the pulse CO2 laser at the oscillation stage enters the CW—CO2 lasers at the amplification stage, and then is amplified while traveling through the CO2 gas laser, so that a laser beam having good convergence and a higher energy is produced from the CW—CO2 lasers at the amplification stage.
Also, it is demonstrated that when two 5 kW rated lasers and one 15 kW rated laser as oscillators are connected in series to amplify a pulsed laser having an average input power of 10 W and a pulse width of 15 ns, the amplified pulse has an average output power of about 2 kW (See, e.g., Non-patent Document 2).